Burglar alarms



J.-G. SEELY BURGLAR ALARMS May 7, 1957 Filed April 18, 1955 INVENTOR. JHMEfi 6-. 5554? BY fizz/2 United States Patent BURGLAR ALARMS James G. Seely, Cudahy, Wis.

Application April 18, 1955, Serial No. 502,152

1 Claim. (Cl. 340-274) This invention relates to improvements in bur-glar alarms, and more particularly to a novel burglar alarm adapted for application to the knob of a door.

An object of the invention is to provide a device of the type which may readily be placed over a door knob and which may be set so that slight rotation of the door knob will set off the alarm.

Other and further objects of the invention will appear as the description proceeds, reference being had to the accompanying drawing, in which:

Fig. 1 is a side view partly in section and partly in elevation of a burglar alarm embodying the invention applied to a conventional door knob.

Fig. 2 is a plan view of the same showing the latch means.

Fig. 3 is a view in vertical section of the device taken from the front.

Fig, 4 is a similar fragmentary view showing the switch in closed position.

Referring more particularly to the drawings, the numeral refers to the device generally, comprising a casing 11 containing a battery receptacle 12. A cover 13 is hinged at 14 of the receptacle 12. The battery 15 is held between the terminal end clamps 16 and 17. A bracket 18 carries the clamps.

The top 19 of the casing 11 has a transversely elongated aperture at 20 which is spanned by the pin 21 on which an inverted T-bar is pivoted. The T-bar 22 has a resilient insert 23 along the lower edge thereof. The casing 11 and the T-bar are formed of metal and the latter acts as a switch. A metal plate 24 is disposed in- Patented May 7, 1957 ternally of the top 19 and is spaced therefrom by the layer of insulating material 25. The alarm signal means 26 is fixed to bracket 18.

A wire 27 connects end clamp 16 with the alarm signal means 26 which is grounded to the casing 11. A wire 28 connects the end clamp 17 with the plate 24.

The casing 11 in the front wall 29 thereof has an aperture 30 sutficiently large to admit a door knob 31.

In use, the casing is hung over a door knob in such a way that the resilient insert 23 rests on the top of the door knob 31, as shown in Fig. 3, the inverted T-bar being in vertical position, the electrical circuit thus remaining open. As soon as the outer door knob 32 is rotated, the T-bar pivots on the pin 21 and makes contact with the plate 24 thus closing the circuit. The resilient strip 33 along the lower margin of wall 29 tends to keep the device 10 from swinging with the rotation of 'the knobs.

A latch 34 is held with a sliding fit at 35 of the top 19 of the casing 11.

It will be understood that the device is capable of many modifications in structure and design, without departing from the spirit of the invention, within the scope of the appended claim.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent of the United States is:

A burglar alarm including a casing having an aperture in a wall thereof adapted to admit a metal door knob, an inverted metal T bar pivoted in the top of said casing adapted to rest on the top of said knob to suspend said casing, a metal contact plate disposed within the casing top, a battery in the casing, an electric alarm means therein, a resilient strip embedded in the lower edge of the cross member of said T bar, and an electric circuit adapted to be closed by contact of the metal door knob with the T bar and the contact plate when said knob is rotated to sound the alarm.

References Cited in the file of this patent UNITED STATES PATENTS 843,904 Mahla Feb. 12, 1907 1,096,935 Miesse May 19, 1914 1,484,502 James Feb. 19, 1924 2,640,894 Krueger June 2, 1953 

